A polycarbonate is a resin excellent in mechanical properties such as impact resistance as well as in transparency and thus has been widely used. In particular, a polycarbonate has found wide application to optical disc for use in optical data recording medium which allows data reproduction and rewriting using laser beam such as audio disc, laser disc, optical disc memory and optomagnetic disc.
The industrial production of such a polycarbonate is normally accomplished by an interfacial polymerization process involving the reaction of bisphenol A with phosgene in a methylene chloride solvent. However, since this process requires the use of phosgene and methylene chloride, which can difficultly be handled on an industrial basis, a process for the production of a polycarbonate which comprises subjecting an aromatic dihydroxy compound such as bisphenol A and a carbonic acid diester such as diphenyl carbonate as starting materials to ester exchange reaction (melt polymerization) in the absence of solvent rather than using these difficult compounds has recently been partly industrialized (Japanese Patent Laid-Open No. 1988-51429, Japanese Patent Laid-Open No. 1990-153925, Japanese Patent Publication No. 1994-99552).
The polycarbonate produced by the aforementioned ester exchange reaction can be used to produce a compact disc (CD). However, CD produced from the polycarbonate obtained by ester exchange reaction disclosed in U.S. Pat. No. 5,606,008 generates a high negative static charge (typically less than −2.0 kV). This high negative static charge can cause the formed product to attract dust, deteriorating the final quality of such a disc. Further, this high static charge causes discs to attract each other. Thus, these discs are stuck to each other in transport, e.g., during conveyance from the injection machine, possibly causing the suspension of production step or the drop of yield. Moreover, this high static charge causes the polycarbonate more wettable during coloring matter coating, causing more defectives in coloring matter coating. In the case of use for CD wherein a rewritable substrate is spin-coated on the surface of a disc, a low negative static charge is required to cause the rewritable layer uniformly wettable.
In order to solve these problems, a method has been disclosed which comprises the use of an aromatic polycarbonate produced by ester exchange reaction to suppress a high negative static charge during production of CD. For example, Japanese Patent Laid-Open No. 1987-207358 and Japanese Patent Laid-Open No. 1999-279396 disclose the incorporation of an antistatic agent in an aromatic polycarbonate.
Further, U.S. Pat. No. 6,022,943 discloses an attempt to reduce the amount of terminal OH groups to not more than 10 mol % based on the total amount of terminal groups by predetermining the molar ratio of diester carbonate to aromatic dihydroxy compound higher than normal. However, this approach gives little or no effect of addition of antistatic agent. Further, even when the amount of terminal OH groups is reduced, no solutions can be given to the problems. An essential solution has thus been keenly desired.